The proportion of officers varies greatly. Commissioned officers typically make up between an eighth and a fifth of modern armed forces personnel. In 2013, officers were the senior 17% of the British armed forces,[1] and the senior 13.7% of the French armed forces.[2] In 2012, officers made up about 18% of the German armed forces,[3] and about 17.2% of the United States armed forces.[4]

Historically, however, armed forces have generally had much lower proportions of officers. During the First World War, fewer than 5% of British soldiers were officers (partly because World War One junior officers suffered very high casualty rates). In the early twentieth century, the Spanish army had the highest proportion of officers of any European army, at 12.5%, which was at that time considered unreasonably high by many Spanish and foreign observers.

Within a nation's armed forces, armies (which are larger) tend to have a lower proportion of officers, but a higher total number of officers, while navies and air forces have higher proportions of officers, especially since military aircraft are flown by officers. For example, 13.9% of British army personnel and 22.2% of the RAF personnel were officers in 2013, but the army had a larger total number of officers.[1]

Having a command authority is one requirement for combatant status under the laws of war, though this authority need not have obtained an official commission or warrant.[5] In such case, those persons holding offices of responsibility within the organization are deemed to be the officers, and the presence of these officers connotes a level of organization sufficient to designate a group as being combatant.

In the United Kingdom, there are three routes of entry for British Armed Forces officers. The first, and primary route are those who receive their commission directly into the officer grades following completion at their relevant military academy. In the second method, an individual may gain their commission after first enlisting and serving in the junior ranks, and typically reaching one of the senior non-commissioned officer ranks (which start at sergeant (Sgt), and above), as what are known as 'direct entry' or DE officers (and are typically and informally known as an 'ex-ranker'). The third route is similar to the second, in that they convert from an enlisted to a commission; but these are only taken from the highest ranks of SNCOs, and are known as 'late entry' or LE officers. LE officers, whilst holding the same Queen's commission, generally work in different roles from the DE officers. In the infantry, a number of warrant officer class 1s are commissioned as LE officers.

Newly commissioned U.S. Navy and Marine Corps officers celebrate their new positions by throwing their midshipmen covers into the air as part of the U.S. Naval Academy class of 2005 graduation and commissioning ceremony.

Commissioned officers are typically the only persons, in an armed forces environment, able to act as the commanding officer (according to the most technical definition of the word) of a military unit.[6] A superior officer is an officer with a higher rank than another officer, who is a subordinate officer relative to the superior.

Non-commissioned officers (NCOs), to include naval and coast guard petty officers and chief petty officers, in positions of authority can be said to have control or charge rather than command per se (although the word "command" is often used unofficially to describe any use of authority).

Most officers in the Armed Forces of the United States are typically commissioned through one of three major commissioning programs:

Graduates of the United States service academies attend their institutions for no less than four years and, with the exception of the USMMA, are granted active-duty commissions immediately upon completion of their training. They make up approximately 20% of the U.S. armed forces officer corps.

ROTC is composed of small training programs at several hundred American colleges and universities.[7] There is no Marine Corps ROTC program per se, but there exists a Marine Corps Option for selected midshipmen in the Naval ROTC programs at civilian colleges and universities or at non-Federal military colleges such as The Citadel and the Virginia Military Institute.[8]

The Coast Guard has no ROTC program, but does have a Direct Commission Selected School Program for military colleges such as The Citadel and VMI.[9]

A smaller number of officers may be commissioned via other programs, such as the Marine Corps Platoon Leaders Class (PLC) during summers while attending college. PLC is a sub-element of Marine Corps OCS and college and university students enrolled in PLC undergo military training at Marine Corps Officer Candidate School in two segments: the first of six weeks between their sophomore and junior year and the second of seven weeks between their junior and senior year. There is no routine military training during the academic year for PLC students as is the case for ROTC cadets and midshipmen, but PLC students are routinely visited and their physical fitness periodically tested by Marine Corps Officer Selection Officers (OSOs) from the nearest Marine Corps officer recruiting activity. PLC students are placed in one of three general tracks: PLC-Air for prospective Marine Naval Aviators and Marine Naval Flight Officers; PLC-Ground for prospective Marine infantry, armor, artillery and combat support officers; and PLC-Law, for prospective Marine Corps judge advocate general officers. Upon graduation from college, PLC students are commissioned as active duty 2nd Lieutenants in the US Marine Corps Reserve, with the option to augment their commissions to the Regular Marine Corps after five to ten years of commissioned service.

In addition to ROTC, Army National Guard (ARNG) officers may also be commissioned through state-based Officer Candidate Schools. These schools train and commission college graduates, prior-servicemembers, and enlisted Guard soldiers specifically for the National Guard.

Although significantly represented in the retired senior commissioned officer ranks of the US Navy, a much smaller cohort of current active duty and active Reserve officers (all of the latter being Captains or Flag Officers as of 2017) were commissioned via the Navy's since discontinued Aviation Officer Candidate School (AOCS) program for college graduates. AOCS focused on producing line officers for Naval Aviation who would become Naval Aviators and Naval Flight Officers upon completion of flight training, followed by a smaller cohort who would become Naval Air Intelligence Officers and Aviation Maintenance Duty Officers. Designated as Aviation Officer Candidates (AOCs), individuals in the AOCS program were primarily non-prior military service college graduates, augmented by a smaller cohort of college-degreed Active Duty, Reserve or former enlisted personnel. In the late 1970s, a number of Air Force ROTC graduates who had lost their flight training slots prior to going on active duty due to a post-Vietnam Reduction in Force (RIF) resigned their inactive USAF commissions and also attended AOCS for follow-on naval flight training. AOCs were active duty personnel in pay grade E-5 (unless having held a higher Active Duty or Reserve enlisted grade) for the duration of their 14-week program. Upon graduation, they were commissioned as Ensigns in the then-US Naval Reserve on Active Duty, with the option to augment their commissions to the Regular Navy after 4 to 6 years of commissioned service.

AOCS also included the embedded Aviation Reserve Officer Candidate (AVROC) and Naval Aviation Cadet (NAVCAD) programs. AVROC was composed of college students who would attend officer training in two segments similar to Marine Corps PLC, but would do so between their junior and senior year and again following graduation, receiving their commission upon completion of the second segment. NAVCADs were enlisted personnel who held associate degrees, but lacked bachelor's degrees. NAVCADs would complete the entire AOCS program, but would not be commissioned until completion of flight training and receiving their wings. After their initial operational tour, they would be assigned to a college or university full-time for no more than two years in order to complete their bachelor's degree. AVROC and NAVCAD were discontinued when AOCS was merged into OCS in the mid-1990s.

Another discontinued commissioning program is the Air Force's Aviation Cadet program. Originally created by the US Army Signal Corps in 1907 to train pilots for its then-fledgling aviation program, it was later used by the subsequent US Army Air Service, US Army Air Corps and US Army Air Forces to train pilots, navigators, bombardiers and observers through World War I, the interwar period, World War II, and the immediate postwar period between September 1945 and September 1947. With the establishment of the US Air Force as an independent service in September 1947, it then became a source for USAF pilots and navigators. Cadets had to be between the ages of 19 and 25 and possess either at least two years of college/university level education or three years of a scientific or technical education. In its final iteration, cadets received the pay of enlisted pay grade E-5 and were required to complete all pre-commissioning training and flight training before receiving their wings as pilots or navigators and their commissions as 2nd Lieutenants on active duty in the US Air Force Reserve on the same day. Aviation cadets were later offered the opportunity to apply for a commission in the Regular Air Force and attend a college or university to complete a 4-year degree. As the Air Force's AFROTC and OTS programs began to grow, and with the Air Force's desire for a 100% college-degreed officer corps, the Aviation Cadet program was slowly phased out. The last Aviation Cadet Pilot graduated in October 1961 and the last Aviation Cadet Navigators in 1965. By the 1990s, the last of these officers had retired from the active duty Regular Air Force, the Air Force Reserve and the Air National Guard.

In Commonwealth nations, commissioned officers are given commissioning scrolls (also known as commissioning scripts) signed by the Sovereign or the Governor General acting on the monarch's behalf. Upon receipt, this is an official legal document that binds the mentioned officer to the commitment stated on the scroll.

Non-commissioned members rise from the lowest ranks in most nations. Education standards for non-commissioned members are typically lower than for officers (with the exception of specialised military and highly-technical trades; such as aircraft, weapons or electronics engineers). Enlisted members only receive leadership training after they are promoted to positions of responsibility, or as a prerequisite for such. In the past (and in some countries today but to a lesser extent), non-commissioned members were almost exclusively conscripts, whereas officers were volunteers.

In some branches of many armed forces, there exists a third grade of officer known as a warrant officer. In the armed forces of the United States, warrant officers are initially appointed by the Secretary of the service and then commissioned by the President of the United States upon promotion to chief warrant officer. In many other countries (as in the armed forces of the Commonwealth nations), warrant officers often fill the role of very senior non-commissioned officers. Their position is affirmed by warrant from the bureaucracy directing the force—for example, the position of regimental sergeant major in regiments of the British Army is held by a warrant officer appointed by the British government.

A Canadian warrant officer on parade.

In the U.S. military, a warrant officer is a technically-focused subject matter expert, such as helicopter pilot or information technology specialist. There are no warrant officers in the U.S. Air Force; the last warrant officers retired in the 1980s, and ranks became dormant. All other U.S. Armed Forces have warrant officers, with warrant accession programs unique to each individual service's needs. Although Warrant Officers normally have more years in service than regular commissioned officers, they are below regular commissioned officers in the rank hierarchy. In certain instances, commissioned chief warrant officers can command units.

A non-commissioned officer (NCO) is an enlisted member of the armed forces holding a position of some degree of authority who has (usually) obtained it by advancement from within the non-commissioned ranks. Officers who are non-commissioned usually receive management and leadership training, but their function is to serve as supervisors within their area of trade specialty. Senior NCOs serve as advisers and leaders from the duty section level to the highest levels of the armed forces establishment, while lower NCO grades are not yet considered management specialists. The duties of an NCO can vary greatly in scope, so that an NCO in one country may hold almost no authority, while others such as the United States and the United Kingdom consider their NCOs to be "the backbone of the military" due to carrying out the orders of those officers appointed over them.[11]

In most maritime forces (navies and coast guards), the NCO ranks are called petty officers while enlisted ranks prior to attaining NCO/petty officer status typically known as seaman, or some derivation thereof. In most traditional infantry, marine and air forces, the NCO ranks are known as sergeants and corporals, with non-NCO enlisted ranks referred to as privates and airmen.

However, some countries use the term commission to describe the promotion of enlisted soldiers, especially in countries with mandatory service in the armed forces. These countries refer to their NCOs as professional soldiers, rather than as officers.

Officers in nearly every country of the world are segregated from the enlisted soldiers, sailors, airmen, marines and coast guardsmen in many facets of military life. Facilities accommodating needs such as messing (i.e., mess hall or mess deck versus officers mess or wardroom), separate billeting/berthing, domiciles, and general recreation facilities (officer clubs versus NCO Clubs and CPO Clubs versus enlisted clubs) are separated between officers and enlisted personnel. This class system, historically correlated to socioeconomic status, is focused on discouraging fraternization and encouraging professional and ethical relations between officers and enlisted military personnel.[12]

Officers do not routinely perform physical labor; they typically supervise enlisted personnel doing so, either directly or via non-commissioned officers. Commissioned officers will and do perform physical labor when operationally required to do so, e.g., in combat. However, it would be very unusual for an officer to perform physical labor in garrison, at home station or in homeport.